1. Field of the Invention
The present invention relates to control circuits, and particularly to a voltage regulator module control circuit.
2. Description of Related Art
In order to deliver a highly accurate supply voltage to microprocessors, a dedicated DC/DC converter is usually placed in close physical and electrical proximity to the processor or other chip or module having such requirements. Such a converter is often provided in a modular form and is referred to as a voltage regulator module (VRM). Most common of the currently used VRM circuit topologies are multiphase (e.g. two or more phases) buck converters, the principal benefits of which are ripple voltage cancellation effect, efficiency, relatively small module size, and the ability to use relatively inexpensive components. More specifically, the ripple cancellation effect between the phases allows use of small inductances to improve transient response and minimization of output filter capacitance.
Use of more than two phases can interleave the conductor currents between the individual phase channels and thereby greatly reduce the total ripple currents flowing into the output capacitors. Such further reduction of ripple current by use of three or more phases allows use of even smaller inductors to improve transient response and allows for a small capacitance to meet transient requirements. Reduced ripple voltage also allows for more voltage deviation during transients because the ripple voltage will consume less of the voltage tolerance budget.
However, a three phase VRM can work normally when one phase thereof is not available. Therefore, the remaining two phases of the VRM which are provided to the microprocessor draw more current. It is dangerous for the VRM to drive the microprocessor with only two phases, because the heavy current may damage the VRM or reduce stability of the VRM.
What is needed, therefore, is a VRM control circuit which can solve the above problem.